how can find with this field.

[ankitbavadiya]

db.test.insert({"_id":1, "marks.m1" : 78})
it is insert with no error in mongo shell but when ever i find data with this (.)dot sign field then it gives null
like
db.test.find({"marks.m1":78})
here i am not talk about embedded field. but i talk about just field name.